The present invention relates to a resin-coated paper type support for imaging materials which comprises a paper mainly composed of natural pulp as a base, one side of the paper base (hereinafter sometimes referred to as "base paper") on which an image forming layer is provided being coated with a resin layer (A) containing a resin having film-formability and another side of the paper base being coated with a resin layer (B) mainly composed of a polyethylene resin. More particularly, it relates to a resin-coated paper type support for imaging materials which can provide imaging materials and prints obtained therefrom which are high in gloss appearance, especially, silver halide photographic papers and prints obtained therefrom (print of silver halide photographic paper is sometimes referred to as merely "photographic print" hereinafter), and is superior in cutting properties and curling properties.
Usually, an imaging material comprises a support for the imaging material and an image forming layer provided on the support. For example, silver halide photographic materials, ink jet recording materials, thermal diffusion transfer type thermal transfer recording image materials, heat-sensitive recording materials, and photosensitive-thermosensitive recording materials comprise a support for imaging materials and, coated thereon, an image forming layer such as a silver halide photographic layer, an ink imaging layer, heat-migration type heat transfer recording image layer, a heat-sensitive color forming layer, or a photosensitive heat-sensitive color forming layer, and, if necessary, auxiliary function layers such as a subbing layer, a protective layer and a back layer. Especially, the silver halide photographic layer comprises a silver halide photographic emulsion layer, a protective layer, a subbing layer, an intermediate layer, a color-mingling inhibition layer, an antihalation layer, a filter layer, an ultraviolet absorbing layer, a backing layer and combination thereof. For example, a single silver halide photographic material comprises a support for the photographic material and, provided thereon, a silver halide photographic emulsion layer and a protective layer therefor. Furthermore, a multi-layer silver halide color photographic material comprises a support for the photographic material and, provided thereon in succession, silver halide color photographic constituting layers such as a subbing layer, a blue-sensitive silver halide photographic emulsion layer and an intermediate layer, a green-sensitive silver halide photographic emulsion layer and an ultraviolet absorbing layer, a red-sensitive silver halide photographic emulsion layer and a protective layer.
Hitherto, there has been well known a resin-coated paper type support comprising a base paper coated with a resin having film-forming ability. As supports for silver halide photographic materials, for example, JP-B-55-12584 discloses a technique on supports for photographic materials comprising a base paper coated with a resin having film-forming ability, preferably a polyolefin resin. U.S. Pat. No. 3,501,298 discloses a support for photographic materials which comprises a base paper the both sides of which are coated with a polyolefin resin. Furthermore, since the rapid photographic development process has been applied to silver halide photographic materials, supports for photographic materials which comprise a base paper coated with a polyethylene resin on both sides have been practically used as supports for photographic papers, and, if necessary, the resin layer on the side on which an image forming layer is provided usually contains a titanium dioxide pigment to impart sharpness to images.
Moreover, U.S. Pat. No. 4,774,224 proposes a thermal transfer imaging element having as a support a resin-coated paper of 7.5 microinch-AA or less in surface roughness of the resin coat, particularly, a polyethylene resin-coated paper comprising a base paper coated with a polyethylene resin on the surface. In addition, JP-A-63-307979 discloses an ink jet recording sheet having a resin-coated paper as a support.
However, resin-coated paper type supports for imaging materials which comprise a base paper, especially, a base paper mainly composed of natural pulp which is coated with a resin layer on the side on which an image forming layer is provided still suffer from some serious problems and satisfactory results have not yet been obtained.
First, generally, a resin-coated paper used as a support for imaging materials which is coated with a resin layer containing at least a thermoplastic resin, especially a polyethylene resin on the side on which an image forming layer is provided (hereinafter, the side on which an image forming layer is provided is sometimes referred to as "top side", the resin layer coated on the top side is sometimes referred to as "top resin layer", the opposite side is sometimes referred to as "back side", and the resin layer coated on the back side is sometimes referred to as "back resin layer") is produced through a series of steps of casting a polyethylene resin composition in the form of a film on a running base paper from a slit die of a melt-extrusion machine to coat the composition on the base paper, press-bonding them between a press roll and a cooling roll, and peeling the resin-coated paper from the cooling roll. In the case of producing a resin-coated paper for imaging materials which is used for obtaining gloss, as the cooling roll there is used a cooling roll of very high smoothness which has a mirror surface, a glossy surface or a finely rough surface mentioned in JP-B-62-19732. Thus, since the top resin layer of the resin-coated paper in molten state is allowed to press-contact with the cooling roll of very high smoothness, this resin layer is processed to have a surface of high smoothness. As a result, imaging materials having said resin-coated paper as a support and prints obtained therefrom should have a visually high glossiness. However, imaging materials having the resin-coated paper as a support and prints obtained therefrom which were actually produced could not have sufficiently high gloss appearance. Especially, as for photographic papers having the resin-coated paper as a support, there could not be obtained photographic printing papers and photographic prints having sufficiently high gloss appearance.
Therefore, the inventors have made various investigations on the factors for the gloss appearance of imaging materials and prints obtained therefrom, and, as a result, it has been found that as the factors affecting the gloss appearance, there are various factors such as resin-coated paper as a support, image forming layer and image forming methods such as development, but the gloss appearance is also greatly affected by the resin-coated paper as a support. The inventors have made further investigations on the factor of the resin-coated paper affecting the gloss appearance, and as a result, it has been found that the gloss appearance of imaging materials and prints is governed by the factor of resin layer and besides by the factors of kind or properties of the base paper mainly composed of natural pulp, for example, kind and fiber length of natural pulp, stock slurry conditions such as additives for paper contained in stock slurry, paper making conditions such as paper making speed, smoothing press, machine calender conditions, after-treating conditions such as size press and tab size press, and, furthermore, surface roughness of the base paper, and other various factors. Moreover, it has been found that with the decrease in thickness of the top resin layer of the resin-coated paper, especially, in the case of 31 .mu.m or less, the gloss appearance of imaging materials having the resin-coated paper as a support and prints obtained therefrom sharply decreases. Especially, photographic materials for glossy use are required to have a high gloss appearance for prints made from the photographic materials, and photographic materials which give photographic prints of inferior gloss appearance are utterly unsuitable for glossy use and have no commercial value.
Secondly, as for curling properties of imaging materials comprising a resin-coated paper type support and, coated thereon, an image forming layer and auxiliary function layers and those prints obtained from the imaging materials, the imaging materials and prints obtained therefrom preferably somewhat curl in minus (curling with the back side opposite to the image forming layer being inward) or are flat from the points of processability with processing devices in the production of prints from the imaging materials and appearance of the finished prints or pasting of the prints in albums. However, imaging materials having the conventional resin-coated paper as a support and prints obtained therefrom tend to greatly curl in plus (curling with the image forming layer side being inward) to cause problems in processability of the imaging materials, appearance of finished prints and pasting of the prints. The tendency of curling in plus of imaging materials having a resin-coated paper as a support and prints obtained from the imaging materials is mainly due to the contraction of binder contained mainly in the image forming layer and auxiliary function layers, and when gelatin is used as the binder, the tendency is conspicuous especially in silver halide photographic materials using gelatin as a main binder and photographic prints obtained therefrom, and it further became conspicuous especially under the environment of low humidity.
Thirdly, imaging materials comprising a base paper mainly composed of natural pulp which is coated with a resin layer mainly composed of a resin having film forming ability on the side on which an image forming layer is provided and is coated with a resin layer mainly composed of a polyethylene resin on the back side, and prints obtained after image forming treatment, especially, silver halide photographic materials and prints obtained after development treatment, mainly, prints in the form of roll, are cut to a desired size by cutters such as a guillotine cutter and a precision print cutter. In this case, there often occur the problems that the imaging materials or prints cannot be precisely cut and whiskers are formed at the cut surface to reduce commercial value and that they cannot be cut to the desired size. In the worst case, imaging materials and prints made therefrom, especially, silver halide photographic materials and prints thereof can hardly be cut and are bent. These phenomena are seen when photographic prints in the form of roll are cut at a high speed by a precision print cutter and especially when the distance between edges (hereinafter sometimes referred to as "edge width") is set wide.
Therefore, the inventors have made various investigations on the factors for the cutting properties of imaging materials and prints obtained therefrom, and, as a result, it has been found that as the factors affecting the cutting properties, there are various factors such as resin-coated paper as a support, image forming layer, kind of cutters and cutting conditions, and the cutting properties are greatly affected by the factors of the resin-coated paper as a support. The inventors have made further investigations on the factors of the resin-coated paper affecting the cutting properties, and as a result, it has been found that the cutting properties of imaging materials and prints are governed by the factors of resin layer and, besides, by the factors of kind or properties of the base paper mainly composed of natural pulp, for example, kind and fiber length of natural pulp, stock slurry conditions such as additives for paper contained in stock slurry, paper making conditions such as paper making speed, smoothing press, machine calender conditions, after-treating conditions such as size press and tab size press, and, furthermore, stiffness and density of the base paper, and other various factors. Moreover, it has been found that with the increase in thickness of the back resin layer of the resin-coated paper, especially, in the case of 20 .mu.m or more, the cutting properties of imaging materials having the resin-coated paper as a support and prints obtained therefrom are conspicuously deteriorated.
Under the circumstances, when the method of increasing the thickness of the top resin layer which is the commonest and simplest method for improving the smoothness of the resin-coated paper is carried out for improving the gloss appearance of imaging materials and prints for the glossy use which is the first problem, with increase in thickness of the top resin layer, especially, in the case of 31 .mu.m or more, the resin-coated paper, the imaging materials having the resin-coated paper as a support and prints curl with the image forming layer side being inside and, thus, there is caused the second problem of deterioration in curling properties.
Similarly, some technical proposals have been made to improve the gloss appearance. JP-A-61-132949 describes or discloses a technique to provide a photographic support of resin-coated paper type having a strong stiffness and a high glossiness by using a photographic base paper having a first coating layer mainly composed of a low-density polyethylene resin and a second coating layer composed of a polymer having a high stiffness modulus, and as the polymer having a high stiffness modulus, there are exemplified polyolefins such as polycarbonate (PC), high-density polyethylene (HDPE), polypropylene (PP), and linear low-density polyethylene (LLDPE), polyamides such as nylon 11, nylon 6, and nylon 66, and polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). However, this technique is still insufficient for improving the gloss appearance of imaging materials using the resin-coated paper as a support and prints obtained therefrom, and, in addition, the second problem of deterioration in curling properties occurs. That is, when a polymer of high density is used as the polymer in the second coating layer, especially, with increase in density and with increase in content of the polymer in the layer, the resin-coated paper, the imaging materials having the resin-coated paper as a support and prints obtained from the imaging materials are deteriorated in curling properties.
JP-A-7-120868 discloses a technique on resin-coated paper type supports for photographic papers improved in adhesion between a base paper and a water-resistant resin layer and releasability from cooling roll by employing the water-resistant resin coating layer comprising two or more layers and by increasing the density of the layer remotest from the base paper than the density of the water-resistant resins of other layers, and JP-A-7-168308 discloses the attainment of the technique by employing the water-resistant resin coating layer comprising two or more layers and by using a water-resistant resin of a specific flexural modulus as the resin of the outermost layer. However, these techniques are still insufficient for improving the gloss appearance of imaging materials using the resin-coated paper as a support and prints obtained therefrom, and, in addition, the second problem of deterioration in curling properties occurs. That is, when a water-resistant resin of high density is used as the water-resistant resin in the coating layer, especially, with increase in density and with increase in content of the water-resistant resin in the coating layer, the resin-coated paper, the imaging materials having the resin-coated paper as a support and prints obtained from the imaging materials are deteriorated in curling properties.
On the other hand, for the purpose of improving the smoothness of resin-coated paper, JP-A-58-68037 discloses use of pulp having a specific fiber length distribution, JP-A-60-69649 discloses use of pulp having specific fiber length, width and thickness, JP-A-61-35442 discloses use of softwood pulp, JP-A-63-173045 discloses use of specific pulps such as low viscosity pulp, JP-A-58-37642 discloses use of a base paper having a Beck smoothness of higher than a specific value, JP-A-63-291054 discloses use of base papers having specific values of properties such as those having a surface roughness of lower than a specific value, JP-A-60-126397 discloses hot calender treatment of base paper, JP-A-61-284762 discloses employment of paper making method using a paper making machine having an upper dehydrating mechanism, JP-A-63-204250 discloses paper making by two-layer wire paper machine, and JP-A-64-20541 discloses use of specific paper making methods such as stretch press of wet paper. However, these are utterly insufficient for improving the gloss appearance of imaging materials using the resin-coated paper as a support and prints obtained therefrom.
In an attempt to improve the tendency of curling in plus direction of imaging materials and prints which is the second problem, it has often been conducted to contain a high-density polyethylene resin in a large amount in the back resin layer of the resin-coated paper used as a support or increase the thickness of the back resin layer. However, imaging materials using as a support the resin-coated paper containing a large amount of high-density polyethylene resin in the back resin layer or having a thick back resin layer suffer from the third problem of further deterioration in cutting properties.
In order to improve the cutting properties of resin-coated paper type supports, various proposals have been made. JP-A-55-98748 discloses a technique to improve cutting properties of resin-coated paper type photographic supports by using a base paper having a ratio of strengthening agent/sizing agent of 1.8 or more (based on absolute dry weight), preferably a base paper composed of a pulp having a specific nominal size specified in JIS P8207 and containing no long fibers. However, this technique is still insufficient to improve cutting properties of imaging materials having the support, and curling properties of the imaging materials are utterly unsatisfactory. Especially, when the high-density polyethylene resin is contained in an amount of more than 65% by weight in the back resin layer in an attempt to improve curling properties, cutting properties of the imaging materials are further deteriorated.
Furthermore, for the purpose of improving the cutting properties of resin-coated type photographic supports, some techniques on base papers have been proposed. JP-A-63-173045 discloses use of a base paper containing low viscosity pulp, JP-A-63-256788 discloses use of a base paper prepared using a pulp slurry beaten by a specific refiner disk, JP-A-63-306442 discloses use of a base paper composed of a pulp having a specific tensile strength, and JP-A-3-149542 discloses use of a base paper composed of a pulp having an average polymerization degree of 800 or more and an internal bonding power of 1.0-2.0 kgf.multidot.cm. However, these techniques are considerably insufficient to improve cutting properties of imaging materials having the support, and curling properties of the prints are utterly unsatisfactory.
On the other hand, for the purpose of improving the curling properties or the cutting properties of resin-coated paper type photographic supports, some techniques on back resin layer have been proposed. JP-B-48-9963 discloses a photographic support having good curling properties which comprises a base paper coated with a resin composition comprising a low-density polyethylene resin: a high-density polyethylene resin=1:1. Furthermore, JP-A-58-95732 discloses a photographic support of good cutting properties and curling properties which comprises a base paper coated with a polyethylene resin composition comprising 40-75 parts by weight of a high-density polyethylene resin having a density of 0.945 g/cm.sup.3 or more and a melt index of 15-40 g/10 min and 60-25 parts by weight of a low-density polyethylene resin having a density of 0.930 g/cm.sup.3 or less and a melt index of 1-40 g/10 min. Moreover, JP-A-6-230517, JP-A-6-266046 and JP-A-7-36147 disclose photographic supports of good cutting properties and curling properties and showing no formation of gel which comprises a base paper coated with a resin composition comprising a high-density polyethylene resin and a low-density polyethylene resin and having a critical shear rate of lower than a specific value.
However, cutting properties of imaging materials having as a support a resin-coated paper which comprises a base paper coated with a resin composition comprising a high-density polyethylene resin and a low-density polyethylene resin as disclosed in the above prior art are improved to some extent, but are still insufficient if the edge of precision print cutters wears out or the edge width is set somewhat wide (for example, when the edge width is set at 80 .mu.m or more, especially 90 .mu.m or more, further especially 100 .mu.m or more), and, moreover, the cut size of the prints is not precise. Furthermore, cutting properties of imaging materials in which a resin-coated paper having a paper as a base is used as a support are considered to be determined upon entanglement of factors of base paper, resin layer and image forming layer, but these factors have not yet been clarified.